The present invention relates generally to a system for reproducing video signals from a magnetic tape in such a manner of obtaining a slow-motion reproduction picture, or a still reproduction picture, and more particularly to a system for carrying out slow-motion reproduction and still picture reproduction without accompanying any noises or beats on a reproduced picture screen.
The prior art uses a system wherein a video signal is recorded on a magnetic tape on parallel tracks formed obliquely to the longitudinal direction of the magnetic tape. This tape travels at a tape speed which is different from that used at the time of recording or stops thereby to carry out speed-change reproduction such as quick-motion reproduction, slow-motion reproduction, or still picture reproduction. In this system, the tape speed at the time of speed-change reproduction is different from that at the time of recording, therefore the path (track) which the head traces on the tape during reproduction is different from the path (track) traced by the head during recording.
On the one hand, a conventional video signal recording and reproducing system, ordinarily, forms tracks on a recording medium in a manner which leaves an unrecorded zone or band called a guard band between neighboring tracks in order to prevent the generation of beats caused by the reproduced signals of neighboring tracks due to tracking deviation of the head at the time of reproduction. When a tape recorded in this manner is played back by speed-change reproduction as described above, the head traces over the track and the unrecorded band. When the head traces over the unrecorded band, the reproduced signal is remarkably lowered in level or disappears. For this reason, a noise is generated in the reproduced picture. Furthermore, in the above mentioned system, since unrecorded bands are provided between tracks, the utilization efficiency of the tape has been poor.
Accordingly, the present applicant has previously described a system wherein tracks are formed on a tape without gaps between neighboring tracks, and, moreover, a color video signal can be recorded and reproduced without the occurrence of beat disturbance, in the U.S. patent application Ser. No. 731,935 entitled "Color video signal recording and/or reproducing system" filed Oct. 13, 1976, now U.S. Pat. No. 4,178,606, issued Dec. 11, 1979 and assigned to the same assignee as that of this application. In this previously described system, a pair of azimuth heads having gaps which are inclined with a certain azimuth angle in mutually opposite directions with respect to the direction perpendicular to the longitudinal direction of the track are used, and neighboring tracks are formed in contiguous contact side-by-side without a gap therebetween. Furthermore, the phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period, and, moreover, the direction of this phase shifting is reversed from one track to the neighboring track. In accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other, and, moreover, there is no occurrence of beat disturbance.
Then, the present applicant has proposed a new system wherein, in addition to adoption of the above described system, a plurality of rotating heads having gaps the centers thereof in the track width direction being different in height positions with respect to the rotational planes in which the heads travels are used, and the magnetic tape is caused to travel at a speed V which is represented by the equation ##EQU1## wherein Vo is the tape speed for normal reproduction (and recording), and n is a positive or negative integer, or to stop thereby to carry out slow-motion reproduction or still picture reproduction, in the U.S. patent application Ser. No. 892,147 entitled "Video Signal Speed-Change Reproducing System" filed on Mar. 31, 1978, and assigned to the assignee of this application, and subsequently abandoned. A continuation-in-part application Ser. No. 58,818 was filed on July 19, 1979, and issued as U.S. Pat. No. 4,342,053 on July 27, 1982.
This latter proposed system is capable of carrying out slow-motion reproduction or still picture reproduction with least noise. However, the magnetic tape is required to travel at the speed satisfying the above given equation, which gives rise to a problem in that slow motion reproduction at any given speeds can not be carried out. Moreover, when the traveling magnetic tape is to be stopped for still picture production, the position where the magnetic tape stops is not controlled. Accordingly, the operator is required to search the position where the magnetic tape stops with least or no noise while observing the reproduced picture screen. Thus, there arises a problem in that operation becomes rather troublesome.
Accordingly, in the U.S. Pat. No. 4,246,616 in which the assignee is the same as that of the present application, a system for reproducing a video signal in a slow motion or still picture reproduction was proposed, in which the above described problems were overcome.
This previously proposed system for reproducing a video signal in a slow motion or still picture reproduction comprises a tape on which video signals are recorded along video tracks, which extend obliquely to the longitudinal direction of the tape with substantially no space therebetween. A control signal is recorded along a control track extending in the longitudinal direction, the video tracks being recorded by a plurality of rotating video heads having gaps of mutually different azimuth angles. The control signal is recorded along the control track interrelatedly with the recording of the video tracks by the video heads. A motor drives the tape in tape travel or stops the tape. A plurality of rotating, reproducing video heads successively trace the video tracks to pick up and reproduce the recorded video signals. The rotating video heads have gaps which have mutually different azimuth angles that are respectively the same as the first mentioned azimuth angles, and which have different height positions above the plane of rotation of the centers of the tracks in the width direction thereof. The control signals are reproduced from the control track of the traveling tape. A circuit delays the reproduced control signal by a specific time to obtain a delayed signal and uses this delayed signal to stop the motor and therefore the tape travel. The tape is stopped at a position relative to the reproducing video heads at which the reproduction is accomplished so that the time instant when the level of the reproduced video signal becomes a minimum is within or in the vicinity of the vertical blanking period.
According to this previously proposed system, still picture reproduction in the above mode is carried out in a state without generating noise, whereby the slow-motion reproduction is carried out without generating noise as a whole. By selecting the above described still picture reproducing period at will, slow motion reproduction can be carried out at a given slow motion ratio.
Accordingly, when the inertia of the tape moving and driving system including a capstan motor, capstan, and flywheel, is set to a small value, the wow and flutter upon tape moving period in normal recording and reproduction is large, and stable tape movement cannot be performed. Therefore, when measures are taken to stably move the tape, the inertia of the above tape moving and driving system becomes large.
Since the magnetic tape must be stopped at a most suitable position with respect to the video head, there is a limit to the distance (time) between point (time) of detection of the control signal and the point (time) of stopping of the movement, from this point of view. Thus, when the inertia of the tape moving and driving system is large as in the above case, the delay quantity of the above control signal must be exceedingly small. Accordingly, the time constant of the monostable multivibrator which performs the delaying operation must be exceedingly small.
When the above time constant of the monostable multivibrator is set to an exceedingly small value, the time constant can be adjusted towards the positive direction, that is, the time constant can be adjusted towards a direction which increases the value of this time constant, upon adjustment of the reproducing apparatus so that the noise bar is not seen in the reproduced picture according to the inconsistency of the reproducing apparatus. However, adjustment of the time constant towards the negative direction was difficult, that is, adjustment of the time constant towards a direction which decreases the value of this time constant was difficult, since the original value of the time constant is exceedingly small.